Reliability investigation of large area solder joints in power electronics modules and its simulative representation

摘要

Power electronics (PE) modules for inverter units in hybrid/electric vehicles (H/EV) generate a large amount of heat which needs to be dissipated. This is often done via a liquid cooled metallic baseplate which acts as a heat sink. The interconnect between the PE module and the baseplate is realized using a large area lead-free solder joint which under passive temperature cycling (pTC) tests, develops adhesive cracks (delamination) at the solder-intermetallic compound (IMC) interface. Such cracks reduce the capability of the solder joint to effectively transfer heat to the baseplate and potentially lead to device failure due to overheating.Considering the large number of potential designs for various application of such PE modules, an understanding of the influence of the mechanical behaviour of individual assembly components such as the power substrate, baseplate or the solder joint itself on reliability is of great interest and utility. This study therefore provides an in-depth reliability assessment of multiple physical variants aged under three different pTC profiles. The investigation reveals certain clear trends with respect to warpage, stiffness and size of the joining partners. A detailed Finite Element Method (FEM) simulation methodology was also developed that represents the delamination behaviour for lifetime assessment.